1. Field of the Invention
The invention is directed to a mobile crane with a carrier and a superstructure arranged thereon so as to be slewable around a vertical axis, a boom device for lifting a load which is articulated at the superstructure and swivelable around a horizontal axis, and a counterweight arrangement constructed as a superlift device which increases lifting capacity and which is connected to the superstructure in such a way that the counterweight of the superlift device (SL counterweight) can be lifted from the ground to execute slewing movements of the superstructure, wherein the slewing radius of the SL counterweight is changeable, and with an electronic control device for actuating drive units of the mobile crane which is provided with a computing device and with a display and input device for the mobile crane operator for entering data.
2. Description of the Prior Art
Mobile cranes of the type mentioned above are often provided with a crawler chassis and can have a luffing lattice boom. The inclination of the boom can be changed continuously by means of a mast that is arranged at the superstructure in the luffing plane so as to be inclined toward the rear and by rope guying arranged at the mast. The superstructure is normally outfitted with a counterweight. In order to increase lifting capacity, additional ballast can be suspended by the mast in the form of a superlift device as a counterweight to the load to be lifted (SL counterweight). The SL counterweight can be arranged, for example, on a crossarm or on a counterweight carrier which is suspended at the mast by means of a corresponding rope suspension. The horizontal distance between the axis of rotation of the superstructure and the center of gravity of the SL counterweight is referred to as the SL counterweight radius. This applies in a corresponding sense to the term “load radius” as regards the load suspended from the mobile crane. When the superstructure of the mobile crane must execute slewing movements around its vertical axis of rotation with suspended SL counterweight, the counterweight carrier can often follow the slewing movement by controlling the chassis of the counterweight carrier in a corresponding manner. However, this is no longer possible when there are obstacles on the ground within the slewing area. In such cases, just as when the SL counterweight is arranged on a crossarm, the possibility of lifting the SL counterweight off the ground must be ensured under the load conditions of the lifting task at hand without jeopardizing the stability criteria (e.g., standing stability, strength of structural component parts) and the capacity criteria (e.g., rope limits).
When a lifting task is to be performed, the load radius when picking up a load is generally different than the load radius when setting down this load. Accordingly, the load moment sometimes changes considerably during a lifting task. The counterweight moment used for compensating must take this into account and must often be changed when performing a lifting task because, e.g., in case of a substantially reduced load radius, the counterweight moment of the SL counterweight is so overbalanced that it is no longer possible to lift the counterweight to enable slewing movements of the superstructure for reasons of stability. It may be necessary in such cases, for example, to reduce the SL counterweight. However, this entails substantial conversion work. It is often even sufficient to adapt the effective counterweight radius to the changed conditions. The SL counterweight is frequently connected to the superstructure by a telescoping rod which extends essentially horizontally or at least flatly and can be changed in length, for example, by a hydraulic cylinder. By retracting or extending the telescoping rod, the SL counterweight can be adjusted to a smaller or greater radius so that a counterweight moment can be adjusted at which the SL counterweight, which is usually on the order of about 30 cm from the ground, can be lifted without difficulty under the actual load moment.
Since the transport of counterweights is cumbersome and expensive, it is generally desirable to transport as little counterweight as possible to the site where the mobile crane is being used. On the other hand, there is often considerable uncertainty about the actual order of magnitude of the load to be lifted. For example, in the case of a processing installation that has been removed from operation, its actual weight may be considerably greater than the earlier, exactly known assembled weight due to the addition of production remainders in the installation. Therefore, corresponding uncertainties must be taken into account when possible in preparing for a lifting task. A planning task of this kind requires great care and consideration of extensive lifting capacity tables just as much as in the actual performance of the lifting task which may require multiple changes in load radius and counterweight radius due to obstacles in the area of the construction site. Because of the substantial risk potential in transporting heavy loads, the safety aspect takes on a very particular significance.